Hepatic alpha 1 and beta adrenergic receptors in various animal species

Plasma membranes were isolated from the livers of various animal species representing the four vertebrate classes: Amphibia, Reptilia, Aves and Mammalia. These liver plasma membranes displayed comparable levels of purity as judged by marker enzyme analysis. The activities of the two marker enzymes, 5'-nucleotidase and gamma-glutamyltranspeptidase displayed striking, and quite different, species-dependent differences, with no apparent relationship to phylogeny. alpha 1 and beta-adrenergic receptors were characterized in isolated liver plasma membranes by radioligand binding techniques. The hepatic beta-adrenergic receptor was found to be expressed in all animals studied; the hepatic alpha 1-adrenergic receptor was absent in Amphibia and Reptilia, co-expressed with the beta receptor in Aves, and dominant over the beta receptor in Mammalia. These results suggest that, in liver, the beta-adrenergic receptor is more primitive while the alpha 1-adrenergic receptor is of a more recent phylogenetic origin. It is proposed that the latter may have evolved in conjunction with hepatic sympathetic innervation.